1. Field of the Invention
The present invention relates to an opening and closing valve to be used in place of a suck back valve. In particular, the present invention relates to an opening and closing valve which makes it possible to avoid liquid drip caused, for example, from a discharge port of a fluid nozzle connected to a fluid outlet side of the opening and closing valve when the valve is closed, so that the thickness of fluid may be stabilized on a surface applied with the fluid.
2. Description of the Related Art
The suck back valve has been hitherto used, for example, in steps of producing semiconductor wafers. The suck back valve has a function to avoid so-called liquid drip in which a minute amount of coating liquid drips from a discharge port of a fluid nozzle connected to a fluid outlet side of the suck back valve to a semiconductor wafer when the supply of the coating liquid to the semiconductor wafer is stopped by operating an opening and closing valve connected to a fluid inflow side of the suck back valve so that the valve is closed.
A conventional suck back valve is shown in FIG. 5. Such a suck back valve is disclosed, for example, in Japanese Utility Model Publication No. 8-10399. The suck back valve 10 comprises a main valve body 18 formed with a fluid passage 16 for communicating a fluid inlet port 12 with a fluid outlet port 14, and a bonnet 20 connected to the top of the main valve body 18.
For example, a coating liquid supply source 23 is connected to the fluid inlet port 12 via an opening and closing valve 21. A diaphragm 26, which is formed of a material such as fluororesin, is displaceably provided in the fluid passage 16. A chamber 17, which is closed by the diaphragm 26, communicates with a passage 19 for supplying and discharging air in the chamber 17 when the diaphragm 26 is displaced. A thick-walled section 22 is formed at a central portion of the diaphragm 26, and a thin-walled section 24 is formed at the circumference of the thick-walled section 22.
A projection 27 is formed at the top of the thick-walled section 22. The projection 27 engages with a recess 29 defined at a lower end of a piston 30. Thus, the diaphragm 26 is connected to the piston 30. A V-packing 32, which slides on the inner wall surface of the main valve body 18 and which functions as a seal, is installed to the piston 30. A spring 34, which always presses the piston 30 upwardly, is provided in the main valve body 18. A compressed air supply port 28 is formed through the bonnet 20. The compressed air supply port 28 is connected to a compressed air supply source 35 via a flow amount control valve 33 for controlling the flow amount to move the thick-walled section 22 in the vertical direction. Reference numeral 36 indicates an adjusting screw for adjusting the flow amount of the coating liquid drawn by the diaphragm 26, by abutting against the piston 30 to control the displacement amount of the piston 30.
The operation of the suck back valve 10 will be schematically described. In an ordinary state, the opening and closing valve 21 is open, and the coating liquid is supplied from the fluid inlet port 12 to the fluid outlet port 14. In this state, the flow amount control valve 33 is controlled to supply the compressed air from the compressed air supply source 35 to the compressed air supply port 28. Accordingly, the pressure of the compressed air causes downward displacement of the piston 30. The diaphragm 26, which is connected to the piston 30, protrudes into the fluid passage 16 as shown by two-dot chain lines in FIG. 5.
When the flow of the coating liquid is stopped in the fluid passage 16, the flow amount control valve 33 is controlled to stop the supply of the compressed air from the compressed air supply source 35 to the compressed air supply port 28. Thus, the piston 30 and the diaphragm 26 are moved upwardly in an integrated manner by the aid of the resilient force exerted by the spring 34. The piston 30 abuts against the forward end of the adjusting screw 36, and its displacement is restricted. A predetermined amount of the coating liquid, which remains in the fluid passage 16, is sucked in accordance with the negative pressure effected by the diaphragm 26. Thus, the liquid drip is prevented at the coating liquid supply port of an unillustrated fluid nozzle connected to the fluid outlet port 14.